(1) Field of the Invention
The present invention generally relates to fuel injection systems for internal combustion engines. More particularly, the invention relates to improved methods and devices for supplying high-pressure diesel fuel for injection into an internal combustion engine. Accordingly, the general objects of the present invention are to provide novel and improved methods and devices of such character.
(2) Description of the Related Art
Fuel-supply systems for internal combustion engines are well known in the art. Recent developments in the fuel injection art have focused on supplying fuel to fuel injectors from a common fuel-supply rail which can reach very high-pressure levels. For example, pressure levels in such systems can vary from 2,000 psi up to about 29,000 psi (i.e., about 138 bars to about 2,000 bars). A fuel injection system of this type is described in co-pending U.S. patent application 09/065,895, filed on Apr. 23, 1998, the contents of which are hereby incorporated by reference. One characteristic of fuel-supply systems of the type shown and described in the incorporated reference is that optimal performance requires that the fuel-pressure from the common rail be varied with engine performance conditions. Thus, while the fuel-pressure in the common rail is generally maintained within a predetermined range, the fuel-pressure will optimally deviate with rapid changes in the engine operating conditions. Fuel-pressure rates of change on the order of 300 bars over a 0.2 second time interval are typically desired during engine operation. Accordingly, an optimal common rail fuel-supply system should be capable of both increasing and decreasing fuel-pressure at least fast enough to meet this pressure change criterion.
While a number of fuel-supply systems currently in use can meet the above-noted pressure change criterion, they all suffer from one deficiency or another. One such fuel system uses a constant displacement high-pressure fuel pump and regulates common rail fuel-pressure by utilizing an electronically controlled actuator to spill excess fuel as necessary. In this system, an electronically controlled spill valve becomes more restrictive when increased fuel-pressure is needed in the common rail. Under the influence of the electronic control unit, the system dumps excess fuel when reduced fuel-pressure in the common rail is desired. Significantly, the system suffers from high parasitic losses at light and mid loads.
In other fuel systems of the type noted above, a variable displacement pump is utilized in conjunction with an electronically controlled spill valve to improve fuel-supply efficiency. However, these systems rely upon expensive electronically controlled dump valves which are used to reduce fuel-pressure in the common rail. Moreover, two levels of electronic control, one for the pump and one for the spill valve, are necessary to efficiently operate the system.
Yet another fuel-supply system of the type noted above utilizes a variable displacement pump and leakage from at least one fuel injector to reduce fuel-pressure in the common rail as necessary. In such a system it is only necessary to provide electronic control over the variable displacement pump. However, the pump of this system is typically unable to obtain fuel-pressure decreases on the order of 300 bars over a 0.2 second time interval at light loads.
Accordingly, there is a need in the art for an inexpensive fuel-pressure-reduction device which permits fuel systems of the nature discussed above to achieve the desired fuel-pressure-reduction rates with a minimum of electronic control and without any complex components. Such a fuel-pressure-reduction device should be both inexpensive and permit efficient engine operation at low, medium and high loads.